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Homework Help: Net Electrostatic Force

  1. Jan 21, 2016 #1
    1. The problem statement: In the figure four particles form a square with edge length a = 2.44 × 10-2 m. The charges are q1 = q4 = 1.06 × 10-15 C and q2 = q3 = q. What is q if the net electrostatic force on particle 1 is zero?
    All variables and given/known data: The given variable are in the statement, but I have calculated and checked some other important variables.
    • Net force acting on particle 1 by particle 4 is 8.45E-18 N.
    • The X component of the force acting on particle 1 by particle 2 is negative 6.00E-18 N.
    • Distance from particle 1 to particle 4 is 0.034507 m.

    2. Relevant equations: Coulomb Force: 11bfec934e963740d4bed02c2062a4e7.png , where k = 8.99E9

    3. The attempt at a solution
    Since I'm using the above equation to solve for q2, I used algebra to set it up as q2 = (F)(r2) / (k)(q1). Once I plugged the numbers I have (6.00E-18)(1.19E-3) / (8.99E9)(1.06E-15). Once I plug all that in the calculator, I'm left with 7.49E-16 C. But supposedly that is the wrong answer. I've checked my math enough to know all the information above "The attempt at a solution" portion is correct, so the problem must lie within this final step... I think.

    Attached Files:

    • Q1.jpg
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  2. jcsd
  3. Jan 21, 2016 #2
    Note that when inputting my final answer I put in negative 7.49E-16 C, because in order for particle 2 and 3 to counteract the forces of particle 4, they must have a negative charge.
  4. Jan 22, 2016 #3
    I was using the wrong distance for r in my final calculation. All is solved.
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